Adhesive to attach a cooling device to a thermal interface

ABSTRACT

A method of providing thermal connection between a thermal cooling device and an integrated circuit package is provided. An adhesive is applied to a thermal interface outside a heat transfer area thereof. The thermal interface is attached to the cooling device. The device to be cooled is attached to the thermal interface.

This application is a continuation patent application of applicationSer. No. 09/158,227, entitled Application of Pressure Sensitive Adhesive(PSA) to Pre-attach Thermal Interface Film/Tape to Cooling Device, andfiled on Sep. 22, 1998 now U.S. Pat. No. 6,315,038.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to the field of cooling electroniccomponents and circuits. More specifically, the present inventionrelates to attaching electronic components to cooling devices.

(2) Description of the Related Art

Cooling devices such as heat sinks or thermal plates are used inconjunction with electronic and microelectronic circuits/components forcooling these circuits/components. Generally, integrated circuitpackages may be cooled by attaching these packages to heat sinks,thermal plates, or other such cooling devices. Heat sinks or thermalplates dissipate the heat generated by the attached integrated circuitpackages during the operation of these circuits. To provide optimal heattransfer, heat sinks or thermal plates are designed to have, generally,a large surface area. A surface area, herein refers to any area of theheat sink or thermal plate in contact with a cooling fluid such as air.The size of the surface area may generally determine the heatdissipating capacity of a heat sink or thermal plate.

Typically, heat sinks have a plurality of fins upwardly extending fromthe base plate. The fins conduct heat from the base plate. Heat isdissipated by a cooling fluid, such as air, flowing through spaceslocated between the fins. Typically, a cooling space defined by the finsis defined by the base plate and the vertical surfaces of two adjacentfins. The cooling fluid flows through the cooling spaces, thereby makingcontact with the fins, removing the heat by thermal dissipation(convection) from the fins, and further driving the dissipated heatoutside the heat sink. Most heat sinks or thermal plates, are attachedto the device to be cooled by way of a base plate. The larger the baseplate the more efficient is the heat transfer between the device to becooled (integrated circuit package) and the cooling device (heat sink orthermal plate).

Generally, a thermal interface such as a film/tape attached between theintegrated circuit package and a base plate may be used to reduce thethermal resistance between the integrated circuit package and the heatsink or thermal plate. A thin layer of pressure sensitive adhesive (PSA)may be applied to the entire thermal interface surface to attach thethermal interface to the heat sink. However, the PSA is not a goodthermal conductor.

It is desirable to provide a way of attaching a thermal interface to acooling device without adding substantial thermal resistance between adevice to be cooled such as an integrated circuit package and a coolingdevice such as a heat sink or a thermal place.

SUMMARY OF THE INVENTION

The present invention provides a method of providing thermal connectionbetween a cooling device and a device to be cooled. An adhesive isapplied to a thermal interface outside a heat transfer area of thethermal interface. The thermal interface is attached to the coolingdevice. The device to be cooled is attached to the thermal interface.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, aspects and advantages of the present invention willbecome more fully apparent from the following Detailed Description,appended claims and accompanying drawings in which:

FIG. 1 illustrates a top view of a thermal interface to which anadhesive is applied according to one embodiment of the presentinvention;

FIG. 2 illustrates a top view of an alternative embodiment of thethermal interface with an adhesive applied along the entire periphery ofthe thermal interface;

FIG. 3 illustrates an exploded cross-sectional view through a number ofdevices to be assembled together according to one embodiment of thepresent invention;

FIG. 4 illustrates a cross-sectional view through a thermal interfacewith a pressure sensitive adhesive (PSA) pattern attached to the thermalinterface near the edges of the thermal interface;

FIG. 5 illustrates a cross-sectional view through a heat sink to whichthe thermal interface, with the PSA pattern applied near the edges ofthe thermal interface, is attached;

FIG. 6 illustrates an integrated circuit package attached to theassembly of the heat sink and thermal interface with the PSA appliednear the edges of the thermal interface;

FIG. 7 illustrates an integrated circuit package attached to theassembly of a thermal plate and thermal interface with the PSA appliednear the edges of the thermal interface; and

FIG. 8 illustrates a flow chart diagram of a method of providing thermalconnection between a cooling device and a device to be cooled accordingto one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, numerous specific details are set forth toprovide a thorough understanding of the present invention. However, onehaving ordinary skill in the art should recognize that the invention maybe practiced without these specific details. In some instances,well-known elements, structures, and techniques have not been shown indetail to avoid obscuring the present invention.

The present invention provides a method of providing thermal connectionbetween a cooling device and a device to be cooled. An adhesive isapplied to a thermal interface outside a heat transfer area of thethermal interface. The thermal interface is attached to the coolingdevice. The device to be cooled is attached to the thermal interface.The embodiment of the present invention avoids utilizing PSA on theentire thermal interface surface. Using PSA on the entire thermalinterface surface would be equivalent to adding in an insulating layer.This would significantly increase the overall thermal resistance betweenthe device to be cooled such as an integrated circuit package and acooling device such as a heat sink or thermal plate. By applying anadhesive outside the heat transfer area of the thermal interface, theembodiment of the method of the present invention contributes toproviding thermal connection between the cooling device and the deviceto be cooled without obstructing a heat transfer area of the thermalinterface.

FIG. 1 illustrates a thermal interface 102 to which an adhesive pattern(hereinafter referred to as “adhesive”) 104 is applied. In oneembodiment according to the present invention, adhesive 104 is apressure sensitive adhesive (PSA) but the present invention is notlimited in scope to a pressure sensitive adhesive implementation ofadhesive 104. Also in one embodiment of the present invention describedherein the PSA 104 is applied alongside two edges 108 of thermalinterface 102. The two strips of PSA 104 have a thickness in a range ofapproximately 0.0125 to 0.025 mm. Thermal interface 102 may be made ofmaterials including silicone, elastomeric materials, or phase-changematerials. One example of a thermal interface material is Chomerics T443film manufactured by Parker Hannifin Corp., Chomerics Division, locatedat 77 Dragon Court, Woburn, Mass. 01888.

The PSA is applied to the periphery of the thermal interface 102 so thata heat transfer area or contact area 106 (shown in dotted lines) remainsexposed. Proper transfer of heat is thus allowed through the thermalinterface between a device to be cooled such as an integrated circuitpackage, for example, and a cooling device, such as a heat sink or athermal plate, for example. The integrated circuit package and thethermal plate are later attached to thermal interface 102. Heat transferarea 106 is equal to or larger than a contact area of the integratedcircuit package that is later attached to the thermal interface.

FIG. 2 shows an alternative embodiment of thermal interface 102 of thepresent invention. PSA pattern 104 is applied along the entire periphery(4 edges 108) of thermal interface 102.

FIG. 3 illustrates an exploded cross-sectional view of an assemblyincluding an integrated circuit package 116, thermal interface 102, PSA104 and a heat sink 118. Thermal interface 102 has a first surface 130to which the integrated circuit package 116 is later attached and asecond surface 132 to which PSA 104 is later attached.

FIG. 4 illustrates an adhesive, such as PSA 104, applied to surface 132of thermal interface 102 which is interfacing between integrated circuitpackage 116 and a cooling device. The cooling device may be a heat sink(as illustrated in the figure), or any other cooling devices such asthermal plates, heat pipes, thermoelectric coolers, water-cooled metalplates, etc.

Two strips of PSA 104 are applied to the thermal interface 102 nearedges 108 of thermal interface 102. The strips of PSA 104 are attachedoutside heat transfer area 106 defined by vertical dotted lines 114 and112, so that the heat emanated from integrated circuit package 116 isefficiently transferred by thermal interface 102 to base plate 120 ofheat sink 118.

Next, thermal interface 102, with PSA strips 104 applied near edgesthereof, is attached to a surface 104 of base plate 120 as illustratedin FIG. 5. The attachment is mainly due to an adhesive surface of PSA104 that makes contact with surface 140 of base plate 120. Note thet PSA104 is is compliable, becoming very thin when thermal interface 102 ispressed and attached to base plate 120 of heat sink 118. Heat may betransfered from the integrated circuit package 116 to the heat sink 118mainly via heat transfer are 106, demarcated by dotted lines 112 and114. Heat transfer area 106 is not covered by PSA 104. The vendor of theheat sink may then ship the assembly, including the heat sink 118 withthe thermal interface 102 attached thereto, to the manufacturer of theintegrated circuit package, for further assembling the integratedcircuit package 116 to the assembly.

FIG. 6 illustrates an integrated circuit package 116 attached to theassembly of a heat sink 118 and of thermal interface 102 attached to theheat sink by way of PSA 104. Integrated circuit package 116 may beattached to the thermal interface 102 by way of screw(s) and/or clip(s)(not shown). Arrows 126 indicate the flow of heat from integratedcircuit package 116 to heat sink 118.

FIG. 7 illustrates an integrated circuit package attached to theassembly of a thermal plate 119 and of thermal interface 102. Thethermal interface 102 has the PSA 104 applied near the edges of thethermal interface.

FIG. 8 illustrates a flow chart diagram of a method of providing thermalconnection between a cooling device and a device to be cooled accordingto one embodiment of the present invention. The method starts at block802 from where it passes to block 804. At block 804 an adhesive isapplied to a thermal interface outside a heat transfer area of thethermal interface. The method then flows to block 806 where the thermalinterface is attached to a cooling device. Next the method flows toblock 808 where the device to be cooled is attached to the thermalinterface.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof. It will however be evidentthat various modifications and changes can be made thereto withoutdeparting from the broader spirit and scope of the invention as setforth in the appended claims. The specification and drawings are,accordingly, to be regarding in an illustrative rather than arestrictive sense. Therefore, the scope of the invention should belimited by the appended claims.

1. An apparatus comprising: a thermal interface material having a firstside to attach to a cooling device, and a second side to receive heatfrom an integrated circuit by contacting the integrated circuit at aheat transfer area; and an adhesive attached to the first side whereinthe adhesive is attached to a portion of the first side that is outsidethe heat transfer area, wherein the adhesive is attached along aplurality of edges of the thermal interface material, and wherein theplurality consists essentially of two.
 2. The apparatus of claim 1,wherein the thermal interface material comprises a film having aphase-change material to change phase by receiving the heat from theintegrated circuit.
 3. An apparatus comprising: a thermal interfacematerial having a first side to attach to a cooling device, and a secondside to receive heat from an integrated circuit by contacting theintegrated circuit at a heat transfer area; and an adhesive attached tothe first side wherein the adhesive is attached to a portion of thefirst side that is outside the heat transfer area, wherein the thermalinterface material comprises a tape or film.
 4. The apparatus of claim3, wherein the adhesive is attached along a plurality of edges of thethermal interface material.
 5. The apparatus of claim 4, wherein theplurality comprises four.
 6. The apparatus of claim 3, wherein theadhesive comprises a pressure sensitive adhesive.
 7. The apparatus ofclaim 3, further comprising the cooling device attached to the firstside of the thermal interface material.
 8. The apparatus of claim 7,further comprising the integrated circuit attached to the second side ofthe thermal interface material.
 9. An apparatus comprising: a thermalinterface material having a first side to attach to a cooling device,and a second side to receive heat from an integrated circuit bycontacting the integrated circuit at a heat transfer area; and anadhesive attached to the first side wherein the adhesive is attached toa portion of the first side that is outside the heat transfer area,wherein the thermal interface material comprises a phase changematerial.
 10. The apparatus of claim 9, wherein the adhesive is attachedalong a periphery of the heat transfer area.
 11. An apparatuscomprising: a phase changing thermal interface material to thermallycouple a cooling device with an integrated circuit, the phase changingthermal interface material comprising: a heat transfer area between theintegrated circuit and the cooling device, a first surface to receivethe heat from the integrated circuit by contacting the integratedcircuit within the heat transfer area, a phase change material to changefrom a solid phase to a liquid phase by absorbing the heat from theintegrated circuit at the first surface, and a second surface to providethe heat to the cooling device by contacting the cooling device withinthe heat transfer area; and an adhesive to attach the thermal interfacematerial to the cooling device, wherein the adhesive is applied to thesecond surface of the thermal interface material outside of the heattransfer area.
 12. The apparatus of claim 11, wherein the thermalinterface material comprises a Chomerics T443 film.
 13. The apparatus ofclaim 11, wherein the adhesive comprises a pressure sensitive adhesive.14. The apparatus of claim 11, wherein the adhesive comprises a striphaving a thickness between about 0.0125 millimeters and 0.025millimeters.
 15. The apparatus of claim 11, wherein the adhesive isattached at a plurality of edges of the thermal interface material. 16.The apparatus of claim 15, wherein the plurality consists essentially oftwo.
 17. The apparatus of claim 11, wherein the adhesive is attachedalong a periphery of the thermal interface material.
 18. The apparatusof claim 11, further comprising the cooling device attached to thesecond surface of the thermal interface material to provide the heat tothe thermal interface material.
 19. An apparatus comprising: a thermalinterface material having a first side to attach to a cooling device,and a second side to receive heat from an integrated circuit bycontacting the integrated circuit at a heat transfer area; and anadhesive attached to the first side wherein the adhesive is attached toa portion of the first side that is outside the heat transfer area,wherein the adhesive comprises a strip having a thickness between about0.0125 millimeters and 0.025 millimeters.